1. Technical Field
This disclosure relates to a limb lengthening intramedullary (IM) nail that includes a telescoping structure and a magnetic actuating mechanism. More specifically, an IM nail is disclosed that includes a telescoping structure with an internal magnet and an external actuating mechanism that includes rotating magnets for non-invasive lengthening (distraction) or shortening (contraction) of the IM nail as needed.
2. Description of the Related Art
A variety of treatments for limb length discrepancies are known. Limb length discrepancies may arise from birth defects, improper bone growth, disease, or trauma. Treatments of leg length discrepancies include the use of shoe lifts and special boots to raise the foot in the equinus position. The field of orthopedics includes other techniques, such as stimulating epiphyseal growth, surgical shortening of the longer limb, and surgical lengthening of the short limb.
Current limb lengthening techniques generally apply Ilizarov's principle of tension-stress, wherein living tissue subjected to slow, steady tension becomes metabolically activated. Hence, upon the creation of a bone gap and a subsequent distraction of the gap, new bone may be formed to generate an increase in length.
In current limb lengthening techniques, bone of the limb is cut, called an osteotomy or corticotomy. The bone begins development of a callus at this location. The two bone portions are then pulled apart by a mechanical device that is surgically attached to the bone. This procedure is called distraction, in which the callus is stretched, thereby lengthening the bone.
The current mechanical devices used for limb lengthening include external fixators in the form of rings, connected by adjustable struts and that are transcutaneously connected to the bone using wires, pins, or screws.
Various length-adjustable IM nails include: shape memory alloys to lengthen a telescopic IM nail; implanted electric motors to provide a distraction force; hydraulic or pneumatic mechanisms or pumps; ratchet mechanisms; magnetically driven gear mechanisms; and some designs exploit movement by the patient to generate the distraction force.